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Description

According to the formula: $arctan(x)=x-\frac{x^3}{3}+\frac{x^5}{5}-\frac{x^7}{7}+...$ and $π=6arctan(\frac{1}{\sqrt{3}})$.
Define the function $arctan(x)$ and find the value of $π$ when the last term is less than $10^{-6}$.

Input Format

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Output Format

The value of $π$ rounded to 10 decimal places.

Sample

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